1. Field
This invention generally relates to the field of electrical measurement, specifically to a method for measuring the output characteristics of an electrical power supply while it is operating in a system. These measurements include those of output current, output voltage, output impedance, and transient response. During the development of electric or electronic equipment it is often necessary to measure these parameters while the power supply it is in actual service, for the purpose of design verification.
2. Prior Art
Characterization of the output of a deployed power source requires knowledge of the electrical current being supplied to the load. Previously, devices which measured electrical current were generally referred to as “ammeters”, “current probes”, or “embedded current sensors” and there were a number of current sensing methods used.
1. CONVENTIONAL AMMETER—The circuit under test is opened, and the ammeter is connected in across the break so that the current in question is forced to flow through the ammeter. Within the ammeter, there is a transducer that converts the magnitude of the current to some kind of visible user display or recordable data. An example of this prior art is the ubiquitous hand-held digital multimeter (DMM), when set up as an ammeter.
2. MAGNETIC CURRENT PROBE—A structure of high permeability material is positioned around or near to the circuit under test in such a fashion that the magnetic field produced by the circuit under test causes a proportional and detectable signal to appear in the detector circuits, which in turn can be converted to a visible user display or recordable data. An example of this prior art is the Tektronix® A6312 Current Probe.
3. EMBEDDED SENSORS are components permanently designed into the circuit under test which always have the current to be measured flowing through them. These can be used to measure that particular current without having to use an ammeter or current probe. For example, a low value resistor may be built into the circuit such that at any time later, measuring the voltage across this resistor with a conventional voltmeter will give an indication of the current flowing through it by the application of Ohms Law. Another example would be an embedded Hall Effect sensor such as the Allegro® ACS713, used in the same way.
4. VOLTAGE ACROSS EXISTING COMPONENT—In this method, the circuit to be tested must have an existing component that is carrying the current of interest, and that has enough impedance so that it is practical to measure the voltage across it, and calculate the current by the application of Ohms Law. This requires that the impedance of the conductor be known with suitable accuracy. An example of this is measuring the DC voltage across an inductor, and using the series resistance of the inductor to calculate the current.